President Park Geun-hye’s bodyguard remained quiet on key issues surrounding Park’s relationship to her close confidante Choi Soon-sil and her alleged negligence of duty over the Sewol ferry disaster during the impeachment trial on Thursday, citing national security and a confidentiality clause.

During the fourth hearing of the trial, the Constitutional Court dismissed the stated reasons as unjustifiable, warning that his refusal could be seen as an attempt to conceal something fishy.

Lee Young-sun, the presidential office’s administrative staff in charge of Park’s security, refused to confirm how many times Choi and Park’s other confidants secretly visited her at the presidential office. Park’s friend of 40 years, Choi is at the center of a massive corruption scandal which led to Park’s impeachment by the parliament on Dec. 9.

“Whether Choi entered the presidential office is not a national secret. Why should the number of times Choi visited Cheong Wa Dae be kept a secret?” said Kang Il-won, the lead justice of the Constitutional Court. “If it is not related to you or your family’s crime, you should testify. The issues surrounding Choi are a crucial point here.”

Lee, suspected of driving Choi in and out of Cheong Wa Dae and closely assisting her, did not confirm whether he saw Choi at the presidential office, saying “I cannot reveal anything related to my job.”

Justice Lee Jeong-mi accused him of committing “perjury” when he denied driving Choi into the presidential office, citing a text message exchanged between him and an arrested ex-presidential aide, Jeong Ho-seong, who is charged with leaking government secrets to Choi.

Lee admitted to having sent the text message, discovered on Jeong’s phone, in which he said that “Choi is coming in.” The message is suggested to mean that Choi is coming into the presidential office – possibly escorted by Lee.

He only admitted that he had first met Choi sometime around the 2012 presidential election, and met her several times at a dressmaker’s shop in southern Seoul while picking up clothes for Park until early 2016.

Allegations have suggested that Lee carried Park’s close friends including Choi and unauthorized doctors in his car to get them into the presidential office without having their identities checked.

Lee also appeared to go back on his earlier statement given during the prosecutorial questioning that he had never delivered money to Choi on behalf of Park. Choi is suspected of paying for Park’s clothes, which could constitute bribery.

Another witness, Ryu Hee-in, former secretary-general of the National Security Council and a member of the parliamentary committee investigating the cause of the Sewol ferry sinking, said that the president was “ultimately” responsible for handling the maritime disaster.

“I cannot understand that the presidential office does not serve as a control tower in cases of disaster, given my past experience (during the Roh Moo-hyun administration),” he said, dismissing Park’s then-security adviser Kim Jang-soo’s claims that the presidential office was not in charge of coping with the accident.

Park’s alleged seven-hour absence and negligence of duty to save people’s lives during the maritime disaster, in which more than 300 people died or went missing, is one of the key elements of her impeachment.

A former CEO and a staff reporter for a local daily also testified on the government’s alleged crackdown on the media outlet since it reported in 2014 on a document revealing Jeong Yun-hoe’s meddling in state affairs and personnel appointments. Jeong is Choi’s ex-husband.

The hearing comes amid growing frustration over delays in court proceedings caused by the continued absence of key witnesses and their reluctance to give detailed testimonies.

Other than the ongoing impeachment trial, Park is facing an investigation by an independent counsel over suspicions that she conspired with Choi and ex-presidential aide An Chong-bum to extort donations and favors from local conglomerates.

Choi’s niece and close associates are all being tried for criminal charges including attempted fraud, abuse of power and coercion.

President Park, Choi, An and Jeong all deny their charges, and even questioning the validity and legitimacy of major pieces of evidence, in what critics see as a tactic to prolong the court proceedings at the Constitutional Court.

But Lee Joong-hwan, Park’s lawyer, said that Park has no intention of delaying court proceedings.

“We are just very busy reviewing more than 40,000 pages of documents,” he said during a briefing Thursday.

Meanwhile, Kwon Seong-dong, chairman of the judiciary committee in the National Assembly, told reporters that the parliamentary committee officially requested Park’s lawyers for explanation on the president’s work from her residence in the presidential office.

“The president’s work from home has no legal grounds and it is illegitimate,” he said.

The request comes after the president submitted to the court a document detailing a timeline for what briefings she received and orders she gave while working at her residence in the presidential office on the day of the ferry sinking.